Pointers and Scales in Measuring Instruments
Instrument scales and pointers may be considered together in
two classes:
(A) Those intended for reading quickly
(in the case of switch board instruments at a distance), and
(B) Those intended for close accurate
reading for portable instruments.
Pointers: The shape and size of the pointers depends upon the type of
instrument. The weight and inertia of pointer must be reduced so as to reduce
the load on the bearing and to avoid necessity of damping torque. The pointer
motion is usually limited by buffer stops little more than the scale. These stops
are constructed as very light springs so that the pointer is not bent when it
strikes them sharply on a sudden overload or reversal of the operating current.
fig 1. Pointer
The pointers for switch board and panel instruments should be
so that the position of the pointer is conspicuous. The pointers are usually
broad or carry broad targets at their ends. Aluminium strip or tube is used for
making pointers and a type arrow head pointer construction is used to give
rigidity.